Photosynthesis

Photosynthesis

1. chloroplasts

   • outer membrane
   • inner membrane
   • stroma
     • light independant
   • thylakoid
     • light dependant
     • lumen acidic
   • grana
   • intergranal lamellae
   • ribosomes for Protein synthesis
   • DNA to code for enzymes
   • starch in stoma as Calvin cycle produces glucose

2. light independant

   • uses rubisco
     • fixes carbon
   • RUBP (5c) in stroma
     • ribulosebisphosphasecarboxylase
       • inefficient
   • RUBP with RUbisco and carbon dioxide
     • 2 molecules of GP (glycerate - 3 phosphase (2x3c)
       • GP can be amino acids
   • GP with ATP and reduced NADP makes TP (triose phosphate)
     • 2 x TP makes a glucose
       • isomerase enzymes to other sugars
       • poymerised to cellulose
       • one TP can make glycerol and this can join with fatty acids from GP to form lipids
   • TP phosphorylated into RUBP and it is regenerated
   • 5/6 GP regenerated into RUBP
   • 6 cycles to make one glucose molecule (6 carbons fixed)
     • 12 TP
       • 2 removed for glucose
       • only 10 regenerated so 10 TP makes 6 RUBP
     • 12GP
     • requires 12 ATP so makes 12 ADP
     • requires 6 reduced NADP so makes 6 NAD

3. light dependant

   • photosystems
     • funnel shape - larger SA for absorbing light
     • photosynthetic pigments
       • primary
         • reaction centre
         • chlorophyll A
       • secondary
         • antenna complex
           • known as light harvesting system
         • accessory pigments
           • chlorophyll B
           • carotenoids
             • carotene
             • xanthophyll
       • range of pigments to absorb the different wavelengths of light
     • how it happens
       • pigments absorb photons in antenna complex
       • electrons are excited and moves to higher energy level and returned (energy released from electrons moving down levels)
       • energy passed from one pigment to another
       • energy passed to reaction centre with chlorophyll a
       • chlorophyll a releases electron into ETC
         • replaced by photolysis
   • photolysis
     • splitting of water with photons
     • 2H2O --> 4H+ + 4e- + O2
     • electrons used to replace electrons in PSII
     • source of protons for chemiosmosis
   • cyclic photophosphorylation
     • only involves PSI
     • small amount of ATP
     • no photolysis
     • no reduced NADP
     • electrons returned to chlorophyll A
   • non-cyclic photophosphorylation
     • PSII and PSI (left to right)
     • electrons from reaction centre passed into ETC with decreasing energies
       • releases energy as electrons move down
         • used to pump protons into thylakoid
     • electrons from ETC replace chlorophyll a in PSI
       • electrons further excited
         • pass out of ETC into stroma
     • concentration gradient of protons, thylakoid membrane impermeable to them
       • pass through chemiosmosis throguh ATP synthase to make ATP by proton motive force
         • photophosphorylation
     • protons in stroma combine with e- to form hydrogen
       • reduces NADP
         • into calvin cycle

4. limiting factors

   • Carbon dioxide concentration
     • limits light dependant
     • less carbon fixation of Rubisco
       • less Gp
         • less TP
           • less RUBP
           • less glucose
     • high
       • low RUBP as converted to GP, carbon dioxide not limiting
       • high GP and TP as lots of carbon fixed
     • low
       • increase as less carbon dioxide fixed
       • low GP and TP as not fixed
   • light intensity
     • limits light dependant
     • less photons for photosystems
       • less electrons for ETC so less ATP made and less reduced NADP
     • bright
       • GP low
         • lots of ATP and reduced NADP so converted to TP
       • TP and RUBP high as enough ATP to convert
     • dim
       • Less ATP and reduced NADP so less GP into TP and RUBP
       • GP high
       • RUBP and TP low as continue to be converted to GP
   • temperature
     • light independant and dependant
     • low temp means lower ROR of Rubisco and ATP synthase
       • high temperature causes denaturation
         • less ATP made
         • less carbon dioxide fixed
           • less GP
             • less TP
               • less RUBP
               • less glucose
       • denaturing of photosystems and membranes, causes pigments to leak
     • low
       • ROR low
       • all enzymes slower
       • concentrations of everything low
     • optimum
       • ROR high, lots of fixation and reactions
       • concentrations of everything high
     • high
       • enzymes denature
       • low concentrations of everything
       • photorespiration occurs instead
   • water stress
     • limits in light independant and dependant
       • less photolysis so less electrons and protons
         • less electrons for ETC so less ATP and reduced NADP
       • stomatal closure
         • less carbon dioxide
           • less carbon fixation
             • less GP and TP so less glucose
   • variable that limits the rate of a process when its at a low level

5. relationship with respiration

   • PSS creates large organic molecules for animals to eat
   • respiration breaks down the large organic molecules into smaller inorganic molecules
   • energy released from breaking bonds in large organic molecules used to make ATP
   • oxygen released from photosynthesis is used in aerobic respiration
   • ATP made in respiration used to drive photosynthsis

6. measuring rate

   • cut leaf disks
     • same SA
     • same plant
     • same leaf
   • add to syringe and suck air out
     • put next to light
       • time for it to rise (oxygen produced so floats
         • rate is 1/t
         • repeat at different LI
     • sodium hydrogen carbonate solution provides carbon dioxide for photosynthesis